Freescale TWR-K70F120M is a module based on Kinetis K70 MCU (Cortex M-4) with plenty of RAM (128MB) to run Linux or uClinux. It is available for 109 USD or 179 USD with Freescale Tower system (TWR-K70F120M-KIT).

I could not find an open source uClinux implementation for Kinetis K70, but emCraft has a Linux Board Support Package (BSP) for the Freescale TWR-K70F120M-KIT hardware platform available for 99 USD.

They have just uploaded a video of Kinetis K70 Tower Kit running uClinux 2.6.33 (with busybox) + u-boot with an ultra fast boot time (about 2 seconds) and showcasing a few capabilities of the system including:

IP stack support

ssh server (dropbear)

http server

nfs support

jffs2 support

Vladimir Khusainov, Founder of Emcraft Systems, also mentioned they benchmarked this setup with drystone:

Linux (uClinux) runs just beautifully on this device. Using ‘dhrystone’, we get about 50% performance we get on a 250Mhz Freescale PowerPC box. Fast boot-up, lots of RAM (the TWR-K70 module provides 128MB of RAM and 256MB of NAND Flash), networking, JFFS2, framebuffer, SSH, HTTPD, Qt/E – all this runs just fine on K70. Overall user experience is your regular “embedded Linux” on an MMU-full microprocessor.